Gunmen attacked and killed six soldiers at a checkpoint in a central Yemeni province as security forces clashed with protesters calling for the president's ouster in a southern city, leaving scores injured, officials and medics said Saturday.

Yemen is reeling from three months of protests demanding longtime President Ali Abdullah Saleh step down. Saleh snubbed a regional initiative to diffuse the crisis by refusing to step down in exchange for immunity from prosecution. Instead he has pressed on with a crackdown on protesters that has killed more than 150 people.

On Saturday, a representative for the mediators in the six-nation Gulf Cooperation Council arrived in Sanaa, the Yemeni capital, in an attempt to revive the proposal. But opposition representatives rejected the last pitch.

In the southern city of Taiz, police fired rubber bullets, live ammunition and tear gas at protesters who had chained three government offices there as part of a civil disobedience campaign, activist Ghazi al-Samai said.

Field doctor Sadeq al-Shujah said 16 people were injured, including two in critical condition. One of them was shot in the neck, he said. The security forces have been trying to clear the protesters from a main street they have occupied, pelting them with rocks and occasionally opening fire.

A large number of shops have closed in Taiz and 11 other cities in response to a call for civil disobedience.

Meanwhile, a Yemeni security official said gunmen killed six soldiers and wounded a seventh in a central province of Bayda. The assailants attacked the soldiers manning a checkpoint in the town of Radda and fled.

The official spoke on condition of anonymity because he isn't authorized to brief the media. Seven Yemeni soldiers died in two ambushes on Friday.